How can my kiln section stay on all the time in my computerized kiln, even when the on/off switch is off?

A:

A Relay May Be Stuck Shut

All computerized kilns use relays to cycle the power on and off to the kiln sections.

If one of those relays sticks shut, power will go to the kiln all the time.

All L&L Kilns relays and contactors are of a type called "normally open", meaning when there is no power coming to their electro-magnetic coil their electric contacts are open and not allowing power through.

If a relay overheats, its contacts they can weld themselves shut causing power to pass through them even when the kiln is off.

How to Tell For Sure

When the kiln is cold, keep the toggle switch off and plug in the kiln.

Can you hear the electricity hum in the elements?

Wait a minute, can you feel heat from any of the elements? If so, which ones? (be careful not to actually touch them).

Whichever elements come on, replace that section's relay.

Additional Actions to Take

Flip the toggle switch back and forth a few times. Sometimes switches can get stuck in between contacts or the contacts can become oxidized. This removes oxidation and makes sure the contacts are making proper contact.

Power relays are one of the most important components in your kiln. They execute the will of the computer controller, giving power to the elements only when requested. These power relays are also mechanical switches which will wear out over time. Worn out relays can be the cause of slow or incomplete firings, error codes (E-1, E-d), etc. Other more obvious signs of relay failure are if a zone is lagging behind in temperature considerably or if you notice an entire ring of elements not heating/glowing.

The surest way to test your relays is by using a multimeter to check input, output, and signal voltage. If you do not have access to a multimeter you can run a paper test, which will give you some indication of whether or not you have a relay out.

Process

One way to check the relays (or bad elements) is to check the temperatures of each zone by pressing "1", "2" and "3" in sequence and recording the temperatures of each thermocouple at intervals over the length of the firing. If one zone is consistently firing at a lower temperature then you probably have either burned out elements or a bad relay.

If the relay does not make a soft clicking noise when the kiln is turned on try turning the kiln off and on and then restarting the program.

Remove panel.

Set your multi-meter the approximately 24 volts AC. Check the voltage coming into the coil of the Power Relay. You can tell which wires these are because they will be the small wires coming from the control. This test will tell you if you are getting power to the relay coil which actuates the relay. Unless the relay is actuated by the control you will get no output from the power side of the relay.

With panel plugged in and firing check output from Power Relay with your digital multi-meter. The meter should be set to the next highest voltage above 240 volts AC. Output should be approximately the rated voltage of the kiln when it is supposed to be calling for power to the elements.

CAUTION: LIVE ELECTRICITY IS INVOLVED WITH SOME OF THESE TESTS. This test should only be done by an experienced person familiar with electricity.

Remove the nuts from the studs that hold the relay in place. Remove old relay and replace with new one.

Visually inspect the wire connectors. Do they look corroded or "cooked"? Are the wires frayed? Any corrosion on the wire itself? If any of this is questionable you should replace the appropriate wires.

Reconnect all wires. Visually inspect to make sure the spade connectors are down as far as they can go and feel to see that they are tight (a gentle tug should not remove one). If they are loose for some reason remove the wire and slightly squeeze the spade connector with pliers to tighten it.

IMPORTANT: The slip on wire connectors cannot be loose or corroded. If there is a bad connection then heat will be generated and the component that they slip onto (relay, terminal strip, etc) may overheat and fail. If you squeeze the slip on terminal to make it tighter–be sure to squeeze it evenly so that one side is not tight and the other loose. If there are any doubts about the integrity of the wire or the connector replace the whole wire or harness.